Is this a fungus?

Folks, this strange thing is growing on one of my vegetable growing boxes. It's growing near the broccoli and some tomatoes. Anyone have any idea of what it is?

A slime mould. Harmless to your plants, it grows on compost, and then climbed up the frame (yes, they can move!) to disperse its spores.

Resin

Thanks, Resin! I appreciate that. Does it drop spores? Should I remove it?

Looks from the photo like it has already released its spores (and it certainly will have by now, a day later). No need to remove it, it's not doing any harm.

Resin

Thanks, Resin!